$ \left(\dfrac{1}{81}\right)^{\frac{1}{4}}$
Answer: Figure out what goes in the blank: $\Big(? \Big)^{4}=\dfrac{1}{81}$ Figure out what goes in the blank: $\Big({\dfrac{1}{3}}\Big)^{4}=\dfrac{1}{81}$ So $\left(\dfrac{1}{81}\right)^{\frac{1}{4}}=\dfrac{1}{3}$